The present invention relates in general to air flow control within a reproduction apparatus, and more particularly to an air flow control for maintaining the optimum efficiency of the cleaning system of an electrostatographic reproduction apparatus.
In typical commercial electrostatographic reproduction apparatus (copier/duplicators, printers, or the like), a latent image charge pattern is formed on a uniformly charged charge-retentive or photo-conductive member having dielectric characteristics (hereinafter referred to as the dielectric support member). Pigmented marking particles are attracted to the latent image charge pattern to develop such image on the dielectric support member. A receiver member, such as a sheet of paper, transparency or other medium, is then brought into contact with the dielectric support member, and an electric field applied to transfer the marking particle developed image to the receiver member from the dielectric support member. After transfer, the receiver member bearing the transferred image is transported away from the dielectric support member, and the image is fixed (fused) to the receiver member by heat and pressure to form a permanent reproduction thereon.
The pigmented marking particles used to develop latent image charge patterns are formed of a resinous powder generally referred to as toner. In transferring the toner to the receiver sheet, because of the nature of the particulate toner material, it is virtually impossible to make a complete transfer. If the residual toner material (and other debris) is not removed from the dielectric support member prior to reuse of the member to form subsequent images, such subsequent images formed on the member will be degraded (e.g., they will contain considerable undesirable background). Moreover, the toner material may scatter throughout the reproduction apparatus to contaminate its internal structure, thus adversely effecting its over-all operation. Accordingly, such reproduction apparatus generally include a device for cleaning residual particulate toner material (and other debris) from the dielectric support member immediately after transfer of image from the dielectric support member to the receiver member.
A typical system for cleaning the dielectric support member of a reproduction apparatus includes a rotating brush contacting the image bearing surface of the dielectric support. A vacuum atmosphere surrounds the brush and draws residual toner material and debris swept up by the brush through a filter arrangement. Over time, the filter becomes loaded with toner material and debris, and the cleaning efficiency of the system decreases. Eventually, the material captured by the filter may be blown out into the reproduction apparatus or its surrounding work space creating a hazardous condition for the machine, its operator, and the surrounding environment. One mechanism for preventing blow out is described in U.S. Pat. No. 4,099,861 (issued Jul. 11, 1978, in the name of Abel). Such mechanism provides for monitoring the cleaning apparatus of the reproduction apparatus and sensing an overload to shut down the reproduction apparatus.
The above described blow out preventing mechanism includes a light source, such as a light emitting diode (LED), placed in the exhaust path of the cleaning apparatus downstream of the filter thereof and an optical sensor positioned to view the light source. As the filter becomes loaded, particulate material permeates the filter and becomes entrained in the air flow through the exhaust path. The optical sensor produces a signal dependent upon the amount of light reaching the optical sensor. Through a comparator circuit, based upon the signal produced by the optical sensor, the concentration of particulate material in the exhaust path can be determined. At a given set point, a signal may be produced indicative of a particular concentration of toner material in the cleaning apparatus exhaust. Such signal may then be used to trigger an appropriate alarm and/or shut down the reproduction apparatus. While such mechanism is effective in preventing the blow out condition, it does not enable the cleaning apparatus to be controlled in a manner which can account for the loss in cleaning efficiency of the system less than a complete failure of the cleaning apparatus.